12v-9v pro mini

All I have is a 12v line that I would like to lower to 10v or even 9v to power a pro mini.
My question is what would be the best way to do that? I did try to power it with just the 12v but the pro mini ran a little hot so I thought that it might be a good idea to lower the voltage a little.


I did try somthing like this

When I check it with the multimeter at the resister and zener diode I got about 11v which is less then the 12v but when I connected the pro mini it did not even turn on Why Is This?


I won't go into why your zener-based approach won't "work", but the best of the cheap alternatives is to look at "buck regulators" on ebay. If you don't want to do that then look at 7809 or 7805-based circuits (for 9V and 5V, respectively.) Pretty easy to implement, but you must get the wires right.

Yes i have used 7805 based circuits befor but i needed something with a smaller footprint this time that is why i am using the promini

es i have used 7805 based circuits befor but i needed something with a smaller footprint this time that is why i am using the promini

The 7809 is a TO-220 package which is 1/2" wide x 3/4" high x 1/8" thick but you would need a HEATSINK

I think the LM7808 would be a better choice but not as easy to find as 7809.
Can you elaborate about the “form factor” issue because if it is a metal box the heatsink/regulator could
be mounted on the outside. Where is your real estate problem ? (a PCB Layout, a case you are planning
to use or a quadcopter or other RC aircraft ?)

On the PCB layout i only have enough room left for about 3 resistors the problem would be the two caps. Is there no way other then the LM7808?

Yes, but it is a Kludge and may or may not work.
Here is how it works:

A PCB is a two dimensional object with components mounted on it.
PCB real estate is space available (or not) on the 2-dimensional sheet.
There is , however a 3rd dimension. If there is space available in the 3rd dimension, you can put three
through hole pads on the PCB in the space you say is enough for two resistors.
These pads are NOT for a COMPONENT ! They are for a "daughter board" supported by three 16 to 18 ga
SOLID COPPER wire standoffs. The daughter bd. contains the 7808 on a heatsink (see pref link) .
The daughter bd. is PARALLEL but suspended by the thick solid copper wire about 1/2 to 3/4" long.
The daughter bd. is the complete regulator circuit pcb with all the support components. Normally this
kind of daughter bd. is mounted on metal or plastic standoffs so the real estate on the MOTHER BD.
is used for the three standoffs, not pads. (the pads were meant to be GND, vin, Vout for regulator circuit. You still need these but often the connection from the daughter bd. to the mother bd. is a twisted
wire cable 1 to 2" long . This way the daughter bd is sucured by metal standoffs and the electrical
connection is done by the three wire twisted or ribbon cable . Male Header pins on both bds makes the
connection simple with female header connectors at both ends of the cable. The daughter bd. is
suspended above the mother bd but parallel. This technique only works if you have 3rd dimension
real estate available. The daughter bd. is stuffed and mounted and the cable added and your good to go.

Thanks raschemmel I will remember this for other projects But I also have to consider cost and this would put me over the desired cost! I have to make about 30 or so of these boards with the voltage converters only a miner part! Or I could just make the PCB board larger then planed, but this too would put me over the cost but if there is no other way then that might just be what I have to do.

There is one other option. OKI semiconductor sell voltage regulator modules that do not require any other support components . I have a 3.3V and a 5V. Both can handle up to 36V dc input and output 1.5A.
They are 3-pin devices. I believe that have an 8V version. I'll look for it and get back to you.

Thanks raschemmel I wish that the OKI semiconductor voltage regulator modules was less, at $4.30 it's a bit high but the only other way I can get it to work is at $2.00 I could use DC-DC LM2596 Step Down Adjustable Converter but I would have to wire it off board and find a place for it! so it looks like I will be ordering the OKI-78SR-5/1.5-W36-C and try it.

Thanks again

Is that going to work for you ?

All I have is a 12v line that I would like to lower to 10v or even 9v to power a pro mini.

You didn't tell us which Pro-Mini you have (3.3V/8Mhz or 5V 16 Mhz?)

If you plan to use it for the Pro-Mini make sure to connect the regulator output to the 5V pin if you have the 5V Pro-Mini and to the Vin pin if you have the 3.3V Pro-Mini. It is a low dropout regulator so the
3.3V version works on any input > 3.35V (Vin pin) and the 5V works on anything >= 5V.

Input Voltage 3.35 -12 V (3.3V model)
5 - 12 V (5V model)

Five SMD diodes in series.

5V 16 Mhz Pro Mini

Paul__B What SMD diodes would I use?

That's an elegant solution if they'll fit. Can't be simpler.

Would 5 of these work?


Click the LINK button in betwee the IMAGE button (the monitor screen) and the EMAIL button (envelope)
Paste the URL link into the FIRST box prompted and click ok
Type in a link label (such as the word "these" into the SECOND box prompted, click ok.

the result :
Would 5 of these work?

Thanks I'll make a note of that!

40V 1A Rectifier Diodes?

40V 1A Rectifier Diodes?

Sorry, that was just a link I used for my explanation of how to post a link... :wink:

Ok I would still like to know if the 40V 1A Rectifier Diodes are the right ones and if I need a resister at the end of the last Diode?

+12v in ---Diode+---Diode+---Diode+---Diode+--Diode+----> RAW Arduino Pro Mini
-12v GND--------------------------------------------------------->GND

Will this work or do I need the resister?